Resample via a libsamplerate (#117)

We need to do this for recording as we can't specify a rate.

We need to do this for playback for sample rates outside of the
browser's supported range. That includes the current default rate for
Firefox and older Safari.

Uses a resampler build that doesn't support medium/best to save on
bundle size.

I've also increased the buffer size so I can play a 44k sample in an
OK-ish way. Maybe 256 will be needed.

We know Firefox on Windows still performs poorly. It did badly with
audio before these changes.

Another significant issue is that it can take 3 seconds to call getUserMedia on Desktop Safari.

README.md

@@ -331,6 +331,26 @@ Steps for WASM debugging in Chrome:
 - Enable "WebAssembly Debugging: Enable DWARF support" in DevTools Experiments
 - DEBUG=1 make
 
+## License
+
+This software is under the MIT open source license.
+
+[SPDX-License-Identifier: MIT](LICENSE)
+
+MicroPython for micro:bit is included in the build process via a submodule.
+
+We use dependencies via the NPM registry as specified by the package.json file under common Open Source licenses.
+
+Full details of each package can be found by running `license-checker`:
+
+```bash
+$ npx license-checker --direct --summary --production
+```
+
+Omit the flags as desired to obtain more detail.
+
+A fork of libsamplerate_js to reduce bundle size is [hosted on GitHub](https://github.com/microbit-foundation/libsamplerate-js).
+
 ## Code of Conduct
 
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